The present invention relates to the clarification of raw water for use in the industrial or domestic applications, or the clarification of wastewater for reuse or disposal. Raw water such as from rivers, lakes, or underground usually contains suspended matter. The suspended matter must be removed by clarification in order to provide water suitable for use in domestic and industrial applications. The suspended matter can consist of large solids, settleable by gravity alone without any external aid and non-settleable material, often colloidal in nature.
Removal of nonsettleable material is generally accomplished by coagulation, flocculation, and sedimentation. In combination, these three processes are referred to as conventional clarification. See the Betz Handbook of Industrial Water Conditioning, 9th edition, 1991, Betz Laboratories, Inc., Trevose, Pa., pages 23 through 30.
Coagulation is the process of destabilization by charge neutralization. Once neutralized, particles no longer repel each other and can be brought together. Coagulation is necessary for removal of the colloidal sized suspended matter. Flocculation is the process of bringing together of the destabilized, or "coagulated" particles to form a larger agglomeration or floc. Sedimentation, or settling, refers to the physical removal of particles from suspension that occurs once the particles have been coagulated and flocculated. Sedimentation alone, without prior coagulation results in the removal of only relatively coarse suspended solids.
Naturally occurring suspended particles are predominantly negatively charged. Polyelectrolytes are traditionally used for influent and wastewater clarification. For low turbidity waters, inorganic polyelectrolytes, such as alum, or organic polyelectrolytes, such as melamine formaldehydes are traditionally employed. For higher turbidity waters, high charge cationic polyelectrolytes such as polyamines formed by the condensation reaction of epichlorohydrin and dimethylamine can be used. High turbidity waters are generally considered those having a greater than 60 NTU (Nepholometric Turbidity Units). In low turbidity waters, those with less than 60 NTU, there are generally not enough particles to form a settleable floc when the water is treated with cationic polymers alone. Inorganic coagulants such as alum, aluminum sulfate, polyaluminum chloride, ferric sulfate, ferric chloride, sodium aluminate and melamine formaldehydes are used either alone or in combination with high charge cationic polyelectrolytes.
The use of inorganic coagulants tends to generate voluminous sludges which are difficult to dewater. Also, such inorganic coagulants are only effective within a particular pH range and therefore require proper pH adjustment of the water during treatment. In addition, the increase of iron and aluminum ions in the treated water from the inorganic coagulants may affect downstream operations such as cooling and boiler treatments and may also cause health and environmental concerns when the water is finally discharged. Similarly, the use of melamine formaldehyde resins can result in residual formaldehyde in the resin causing handling and disposal difficulties.
It is an object of the present invention to provide methods for clarifying water which are more effective than the use of alum, melamine formaldehyde or the reaction product of epichlorohydrin and dimethylamine.
The use of vinylamine copolymers for flocculation in water treatment is known. U.S. Pat. No. 4,217,214 discloses the use of high molecular weight polyvinylamine hydrochloride as a flocculating agent in water treating systems. Polyvinylamine hydrochloride is an ethenamine hydrochloride homopolymer, CAS Registry No. 29792-49-2.
U.S. Pat. No. 4,808,683 discloses the use of a mixture of a vinylamine copolymers of the formula disclosed therein as a flocculating agent, drainage aid and paper strength increasing agent.
U.S. Pat. No. 4,957,977 discloses the use of a mixture of vinylamine copolymers of the formula disclosed therein as a flocculating agent and a paper strength increasing agent.